Renewable diamondoid fuels

ABSTRACT

A method to generate dense, multi-cyclic diamondoid fuels from bio-derived sesquiterpenes. This process can be conducted with both heterogeneous and homogenous catalysts and produces the targeted isomers in high yield. The resulting multi-cyclic structures impart significantly higher densities and volumetric net heats of combustion while maintaining low viscosities which allow for use at low temperature/high altitude. Moreover, bio-derived sesquiterpenes can be produced from renewable biomass sources. Use of these fuels will decrease Navy dependence on fossil fuels and will also reduce net carbon emissions.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a divisional application, claiming the benefit of, parentapplication Ser. No. 61/840,004 filed on Jun. 27, 2013, whereby theentire disclosure of which is incorporated hereby reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

The invention described herein may be manufactured and used by or forthe government of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

FIELD OF THE INVENTION

The invention generally relates to processes for the conversion ofrenewable, bio-derived sesquiterpenes to high density diamondoid fuels,and the resulting fuels have net heats of combustion higher thanconventional petroleum based fuels.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a flow chart showing a chemical scheme for conversion ofsesquiterpenes to diamondoid fuels, according to embodiments of theinvention.

FIG. 2 is a flow chart for producing alkyl-adamantane fuel, according toembodiments of the invention.

FIG. 3 is a continuous-flow chart for producing alkyl-adamantane fuel,according to embodiments of the invention.

It is to be understood that the following detailed descriptions areexemplary and explanatory only and are not to be viewed as beingrestrictive of the invention, as claimed. Further advantages of thisinvention will be apparent after a review of the following detaileddescription of the disclosed embodiments, which are illustratedschematically in the accompanying drawings and in the appended claims.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The invention generally relates to processes for the conversion ofrenewable, bio-derived sesquiterpenes and other isoprenoids to highdensity diamondoid fuels including alkyl-adamantane fuels where theresulting fuels have net heats of combustion higher than conventionalpetroleum based fuels. The invention also generally relates to higherterpenes, including diterpenes and triterpenes, and to functionalizedisoprenoids, but not limited to terpene alcohols, aldehydes, andepoxides, which can also be converted to high-density diamondoid fuels.High density fuels with improved volumetric net heats of combustion(NHOC) compared to conventional fuels can significantly increase therange, loiter time, or payload of a variety of platforms includingmissiles, aircraft, and unmanned systems. Embodiments of the inventiondescribe a process for the conversion of renewable, bio-derivedsesquiterpenes to high density diamondoid fuels. The resulting fuelshave net heats of combustion higher than conventional petroleum basedfuels.

Diamondoids are polycyclic hydrocarbons. Alkyl diamondoids (for example,alkyl-adamantanes) are very attractive for use as high-density fuels dueto their high densities, low freezing points, and low viscosities.Renewable fuels based on acyclic hydrocarbons typically have densitiesthat are below the specifications for common aviation and military fuelsincluding Jet-A, JP-5, JP-8, and F-76. The resulting decrease involumetric net heat of combustion limits the range, loiter time, andpayload of both commercial and military aircraft, as well as missiles,UAVs, and other platforms. Embodiments of the invention describe methodsto generate fuels with properties that meet or exceed those ofconventional petroleum derived fuels. Embodiments of the inventiondescribe methods to generate dense, alkylated, multi-cyclic diamondoidfuels from bio-derived sesquiterpenes. This process can be conductedwith both heterogeneous and homogenous catalysts. The resultingmulti-cyclic structures have densities and volumetric net heats ofcombustion that are significantly higher than state-of-the-art fuels,while maintaining low viscosities which allow for use at lowtemperature/high altitude. Moreover, bio-derived sesquiterpenes can beproduced from renewable biomass sources. Use of these fuels willdecrease Navy dependence on fossil fuels and will also reduce net carbonemissions.

A general chemical scheme for converting isoprenoids to diamondoid fuelis illustrated in FIG. 1 using sesquiterpenes as an example. Thechemistry is as follows. The sesquiterpenes are hydrogenated to generatesaturated hydrocarbons. When the isoprenoids are hydrogenated tricyclicsesquiterpenes, they will have the formula C₁₅H₂₆; hydrogenated bicyclicsesquiterpenes will have the formula C₁₅H₂₈; hydrogenated monocyclicswill have the formula C₁₅H₃₀ and hydrogenated acyclic sesquiterpeneswill have the formula C₁₅H₃₂. The saturated hydrocarbons are thenisomerized with an acidic catalyst to produce diamondoid fuel. Thediamondoid fuel is purified, and/or various cuts are removed forspecific applications, by distillation. The distilled fuel is useddirectly or is formulated/blended for specific fuel applications. Forexample, the alkyl-adamantane fuels of the invention may be blendedwith, but not limited to, Jet A, JP-10, JP-5, F-76, other renewablefuels including fuels derived from biobutene, biohexene, etc. Thealkyl-adamantane fuels that are embodiments of the invention willnormally be a mixture of various alkyl-adamantanes and sesquiterpanes.The amount of sesquiterpane may be in the range of about 1% to 90% ofthe alkyl-adamantane fuel.

Sesquiterpenes are isolated from a renewable source. Sesquiterpenes canbe generated by a biosynthetic process that utilizes sugar, biomasssugars, CO₂, or CO as a carbon source. Synthetic sesquiterpenes can beused and prepared directly from isoprene or from a reaction betweenterpenes and isoprene. Alternatively, sesquiterpenes can be extractedfrom plants using processes that include steam distillation and solventextraction. Sesquiterpenes can be acyclic. Sesquiterpenes can bemono-cyclic and/or polycyclic hydrocarbons. Cyclic sesquiterpenes can begenerated from acyclic sesquiterpenes.

Higher terpenes including diterpenes and triterpenes, can be thermallycracked to form sesquiterpenes. Examples of bio-derived sequiterpenesthat are feedstocks embodied in the invention are, but not limited to,farnesene, cadinene, selinene, humulene, copaene, clovene,alpha-neoclovene, longifolene, zizaene, thujopsene, other tricyclicsesquiterpenes, caryophyllene, isomerized caryophyllene mixtures, otherbicyclic sesquiterpenes, monocyclic sesquiterpenes including bisabolene,and acyclic sesquiterpenes including farnesene. Bio-derivedcyclopentadiene dimers and higher oligomers of bio-derivedcyclopentadienes are also disclosed which includes alkylated versions(i.e. tetrahydrodimethyldicyclopentadiene) which we have shown can begenerated from linalool, myrcene, and some sesquiterpenes.

The following are publications related to topics of the invention. Thebasic properties of petroleum-derived diamondoid-type fuels aredescribed in: Chung, H. S.; Chen, C. S. H.; Kremer, R. A.; Boulton, J.R.; Burdette, G. W. Energy Fuels 1999, 13, 641-649. A recent paper hasdescribed the conversion of functionalized, hydrogenatedcyclopentadienes to diamondoid fuels with ionic liquids: Ma, T.; Feng,R.; Zou, J-J.; Zhang, X.; Wang, Li Industrial and Engineering ChemistryResearch 2013, 52, 2486-2492.

Isoprenoid feedstocks, including sesquiterpenes, are hydrogenated togenerate saturated hydrocarbons. The hydrogenations can be conductedwith either homogenous or heterogeneous catalysts under a hydrogenatmosphere. Hydrogenation catalysts based on nickel, palladium,platinum, ruthenium, and copper are suitable for the reduction. This cantypically be conducted without a solvent. Hydrogenations may beconducted with or without a solvent. In some embodiments, addition of apolar solvent increases the reaction rate and allows for the use ofmilder conditions.

The saturated hydrocarbons are isomerized with acidic catalysts,including a strong Lewis acid or Bronsted acid. Examples of suitableLewis acid catalysts include AlCl₃ and ionic liquids derived from orincluding AlCl₃. Heterogenous Lewis acid catalysts, mesoporousaluminosilicates (e.g. AlMCM-41), and amorphous aluminosilicates, canalso be used. Lewis acidic ionic liquids and fluorinated sulfonic acids(heterogeneous and homogenous) are also suitable acidic catalysts forthe isomerization.

When heterogeneous catalysts are used in a liquid-phase reaction, thehydrocarbon mixture may be separated by filtration, centrifugation,decantation and/or purified by distillation. In the case of homogenouscatalysis, the catalyst may be quenched and the hydrocarbon may beseparated by extraction and/or purified by distillation.

Purified alkyl-adamantane fuels may be used directly as high-densityfuels or formulated with various conventional or renewable fuels togenerate full-performance jet and diesel fuels.

The method shown in FIG. 2 shows a general method for converting anisoprenoid and/or functionalized isoprenoid feedstock to analkyl-adamantane fuel. A first mixture is produced by hydrogenating thefeedstock from about 1 to 48 hours with hydrogen gas at pressuresranging from about 1 atm to about 50 atm using a hydrogenation catalystat temperatures ranging from about 10° to 200° C. An optional polarsolvent may be used in the hydrogenation reactor or hydrogenationreaction zone. The first mixture may optionally be distilled to isolatehydrogenated fuel products, including a sesquiterpane. The first mixtureis isomerized producing a second mixture. The isomerizing is carried outfrom about 0.3 to 48 hours using an acidic catalyst at pressures rangingfrom about 1 atm to about 10 atm at temperatures ranging from about 15°C. to 350° C. The isomerized second mixture is distilled to produce analkyl-adamantane fuel, which is a mixture of alkyl-adamantanes andisomerized sesquiterpanes, or the second mixture is distilled to producespecific aklyadamantanes and/or specific isomerized sesquiterpanes.

Lewis acids, including acidic ionic liquids, are used to isomerizehydrogenated polycyclic hydrocarbons, includingendotetrahydrodicyclopentadiene (endo-THDCPD) to exo-THDCPD, which isthe major component of the synthetic fuel called JP-10. Furthermore,both endo- and exo-THDCPD can be converted to adamantane, the simplestdiamondoid, via skeletal rearrangement (isomerization) using aluminumtrichloride (AlCl₃) as the Lewis acid. The molar fraction of AlCl₃ inthe ionic liquid determines the acidity of the solvent. Increasing thetemperature of the reaction increases the reaction rate and can affectthe percent conversion, selectivity, and ratios of various productsobtained. A reasonable temperature range for the reaction is from 30° to120° C. The fact that ionic liquids phase separate from nonpolarhydrocarbons make ionic-liquid-based methods suitable for continuousflow reaction systems.

A continuous-flow process for producing alkyl-adamantane fuel is anembodiment of the invention. The continuous-flow method shown in FIG. 3uses an isoprenoid and/or substituted isoprenoid feedstock, which mayinclude sesquiterpenes. The feedstock is hydrogenated with hydrogen gasusing a heterogeneous hydrogenation catalyst to produce first productstream, which is then isomerized using a heterogeneous acidic catalystto produce a second product stream. The second product stream isdistilled to produce an alkyl-adamantane fuel. The catalysts of thecontinuous-flow method are supported on fixed beds located in therespective zones. An optional polar solvent may be used, and is fed intothe hydrogenating and isomerizing zone. The first product stream isproduced by hydrogenating the feedstock having a residence time in thehydrogenation zone from about 0.5 to 48 hours with hydrogen gas atpressures ranging from about 1 atm to about 50 atm at temperaturesranging from about 10° C. to 200° C. The first product stream enters theisomerizing zone. The residence time in the isomerizing zone is about0.2 to 48 hours at pressures ranging from about 1 atm to about 10 atmand at temperatures ranging from about 15° C. to 350° C. The secondproduct stream exiting the isomerizing zone is distilled to produce analkyl-adamantane fuel. When an ionic liquid is used, since it isinsoluble in the nonpolar hydrocarbon products formed, it may beisolated from the fuel products and recycled back to the isomerizingzone. Optionally, a solid-state crosslinked ionic liquid-like materialmay be attached to a fixed bed in the isomerizing zone.

Example 1 n-Butyl-1-adamantaneketone

20 g of 1-adamantane carboxylic acid was dissolved in 250 mL THF andthen cooled to −20° C. and while cold 93 mL 2.5 M n-BuLi (2.1 equiv) wasadded slowly dropwise over 1 h. Solids precipitated during this time andthen the mixture was stirred at rt overnight. A standard workupgenerated 20.8 g crude oil. The product was further purified bydistillation under reduced pressure. ¹H (CDCl₃): 2.44 (t, J=7.1 Hz, 2H),2.04 (m, 3H), 1.9-1.63 (m, 12H), 1.59-1.43 (m, 2H), 1.36-1.21 (m, 2H),0.90 (t, J=7.7 Hz, 3H); 13C (CDCl3): 215.84, 46.45, 38.39, 36.78, 35.76,28.16, 25.98, 22.62, 14.10. Analysis calcd for C₁₅H₂₄O: C, 81.76; H,10.98. Found: C, 81.71; H, 11.00.

1-Pentyladamantane

2.3 g of n-butyl-1-adamantane ketone, 5 g hydrazine hydrate, 20 mL ofdiethylene glycol, and 5.6 g KOH were heated to 220° C. for 1 h, broughtdown to 180° C. for 3 h and then left overnight at 130° C. After astandard workup, this procedure gave 2.43 g of crude product (92%).Reduced pressure distillation gave the compound as a colorless liquid.When the reaction was conducted at ten times the scale, a yield of 97%was obtained. The product doesn't freeze when stored at −30° C. ¹H(CDCl₃): 1.93 (m, 3H), 1.79-1.52 (m, 6H), 1.49-1.43 (m, 6H), 1.37-1.17(m, 6H), 1.07-0.97 (m, 2H), 0.89 (t, J=7.2 Hz, 3H); 13C (CDCl3): 45.03,42.82, 37.60, 33.17, 32.48, 29.08, 22.98, 22.29, 14.36. Analysis calcdfor C₁₅H₂₆: C, 87.3; H, 12.7. Found: C, 87.14; H, 12.75.

Example 2

1-Pentyl adamantane, as an example of an alkyl-adamantane fuel, anembodiment of the invention, has a density of 0.946 g/mL, and a net heatof combustion (NHOC), measured by bomb calorimetry, of 145,997 btu/gal(relative standard deviation of 1.3%).

Example 3

Typical hydrogenation conditions for sesquiterpenes. Hydrogenation ofsesquiterpenes including β-caryophyllene, valencene, andpremnaspirodiene was conducted in a Parr shaker without the addition ofsolvent at room temperature and with an overpressure of 40-50 psi ofhydrogen. Either 1 g of 10% Pd/C or 0.1 g of PtO₂ was used for every 100g of sesquiterpene. The bomb was shaken until uptake of hydrogen ceased.The hydrogenation of valencene and premnaspirodiene was complete withintwo hours, while caryophyllene typically required up to 48 hours tofully react. After hydrogenation was complete, the black reactionmixtures were then filtered through a celite pad. Valencane,premnaspirodiane, and caryophyllane were used directly without furtherpurification or were vacuum distilled (85-110° C., 1 Torr) through a 10in Vigreux column to isolate the hydrogenated sesquiterpenes ascolorless oils.

Example 4

Hydrogenation of Longifolane: 100 mL of longifolene, 30 mL of glacialacetic acid, and 0.1 g of PtO2 were added to a glass bomb. The bomb wasplaced under 45 psi hydrogen and shaken at room temperature for two h.The acetic acid was removed in a separatory funnel and the longifolanewas washed with water (2×20 mL) and a 5% sodium carbonate solution. Thelongifolane was then purified by vacuum distillation.

Example 5

Hydrogenated sesquiterpanes are combined with an acid catalyst. Thecatalyst loading, reaction time, and temperature are dependent on thecatalyst type. Some general reaction conditions are listed in Table 1.All reactions are conducted under an inert atmosphere and products werepurified by either physical separation (heterogeneous catalysts) orquenching/extraction (homogenous catalysts) followed by isolation ofeither diamondoids or diamondoid/isomerized sesquiterpane mixtures byfractional distillation.

TABLE 1 Common reaction conditions for isomerization of sesquiterpanesto diamondoid fuels Catalyst Temp (° C.) Time AlCl₃ 150-200 2-4 h Acidicionic liquid  80-120 10 min-several h Heterogeneous catalyst up to 350°C. 1-5 h

Prophetic examples are for illustration purposes only and not to be usedto limit any of the embodiments. Where a range of values is provided, itis understood that each intervening value, to the tenth of the unit ofthe lower limit unless the context clearly dictates otherwise, betweenthe upper and lower limits of that range is also specifically disclosed.Each smaller range between any stated value or intervening value in astated range and any other stated or intervening value in that statedrange is encompassed within the invention. The upper and lower limits ofthese smaller ranges may independently be included or excluded in therange, and each range where either, neither or both limits are includedin the smaller ranges is also encompassed within the invention, subjectto any specifically excluded limit in the stated range. Where the statedrange includes one or both of the limits, ranges excluding either orboth of those included limits are also included in the invention.

Embodiments of the invention generally relate to methods forsynthesizing first alkyl-adamantane fuel including, providing a firstisoprenoid and/or functionalized isoprenoid feedstock, producing firstmixture by hydrogenating the first feedstock with hydrogen gas using atleast one first hydrogenation catalyst, producing a second mixture byisomerizing the first mixture from about 0.3 hours to about 48 hoursusing a first acidic catalyst, and distilling the second mixture toproduce the first alkyl-adamantane fuel. Another aspect of the inventiongenerally relates to continuous-flow methods for synthesizing secondalkyl-adamantane fuel including, providing second isoprenoid and/orfunctionalized isoprenoid feedstock, hydrogenating the second feedstockwith hydrogen gas using second hydrogenation catalyst to produce firstproduct stream, isomerizing the first product stream using second acidiccatalyst to produce second product stream, and distilling the secondproduct stream to produce the second alkyl-adamantane fuel.

In embodiments, in producing the first mixture the hydrogenationcatalyst further includes at least one transition-metal selected fromthe group consisting of, but not limited to, nickel, palladium,platinum, ruthenium, and copper. In embodiments, in producing the firstmixture, the hydrogenating further includes adding at least one polarsolvent selected from the group consisting of, but not limited to, ethylacetate, other organic ester, acetic acid, other organic acid, methanol,ethanol, butanol, THF, dioxane, and other alcohols and alcohols. Inembodiments, the producing the first mixture further includes distillingthe first mixture to produce at least one sesquiterpane. In embodiments,the homogeneous acidic catalyst is selected from the group consistingof, but not limited to, AlCl₃, FeCl₃, TiCl₄, ZnCl₂, SbF₅, BF₃, Lewisacids based on Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Al, B, Sn, Sb invarious oxidation states, and other homogeneous Lewis-acid compounds.

In embodiments, the producing the second mixture by isomerizing furtherincludes adding at least one ionic liquid selected from the groupconsisting of, but not limited to, pyridinium ionic liquid, imidazoliumionic liquid, acidic ionic liquid, acidic chloroaluminate ionic liquid,clay-supported chloroaluminate ionic liquid,[1-butyl-3-methylimidazolium][bis(trifluoromethylsulfonyl imide)],[1-butyl-3-methylimidazolium][tricyanomethanide],[tri(butyl)(tridecyl)phosphonium][bis(trifluoro methylsulfonyl imide)],triethylammonium chloroaluminate, [1-butyl-3-methylpyridinium]chloroaluminate, and [1-butyl-3-methylimidazolium] chloroaluminate. Inembodiments, the acidic catalyst is a heterogeneous Lewis-acid selectedfrom at least one of the group consisting of, but not limited to, AlCl₃,FeCl₃, TiCl₄, ZnCl₂, SbF₅, BF₃, Lewis acids based on Ti, V, Cr, Mn, Fe,Co, Ni, Cu, Zn, Al, B, Sn, Sb in various oxidation states, and otherLewis-acid compound, and where the heterogeneous acidic catalyst issupported on at least one solid material selected from the groupconsisting of, but not limited to, zeolite, aluminosilicate, alumina,zirconia, titania, silica, and clay, other acidic metal oxide,cross-linked sulfonated polystyrene, other macroreticular resin, otherpolymer, crosslinked ionic liquid, crosslinked poly(ionic liquid), andcrosslinked ionic liquid gel.

In embodiments, the producing the first mixture by hydrogenating thefirst feedstock is from about 1 hour to 48 hours with hydrogen gas atpressures ranging from about 1 atm to about 50 atm using the firsthydrogenation catalyst at temperatures ranging from about 10° C. to 200°C. and where the producing the second mixture by isomerizing the firstmixture is from about 0.3 hour to about 48 hours using the first acidiccatalyst at pressures ranging from about 1 atm to about 10 atm attemperatures ranging from about 15° C. to about 350° C. In embodiments,the first alkyl-adamantane fuel produced by the methods herein areincluded in a blended fuel including, but not limited to, Jet A, JP-10,JP-5, F-76, butene oligomer fuels, and hexene oligomer fuels. Inembodiments, the hydrogenating the second feedstock with the secondhydrogenation catalyst is a heterogeneous second hydrogenation catalystsupported on a fixed bed.

In embodiments, the hydrogenating further includes adding at least onepolar solvent selected from the group consisting of, but not limited to,ethyl acetate, other organic ester, acetic acid, other organic acid,methanol, ethanol, butanol, and other alcohols. In embodiments, theisomerizing the first product stream of the second acidic catalyst is aheterogeneous second Lewis acid supported on a fixed bed. Inembodiments, the first alkyl-adamantane fuel is produced by the methodsherein is a blended fuel including Jet A, JP-10, JP-5, F-76, buteneoligomers, and hexene oligomers. In other embodiments, the secondalkyl-adamantane fuel being 1-pentyl adamantane is produced by themethods herein are a blended fuel including Jet A, JP-10, JP-5, F-76,biobutene, and biohexene.

In embodiments, the blended fuel has a density of at least 0.90 g/mL anda NHOC of at least 135,000 Btu/gal. In embodiments, the fuel has acetane number ranging from about 30 to about 42. In embodiments, theblended fuel has a cetane number ranging from about 42 to about 50 andhas from about 1% to about 70% of the alkyl-adamantane fuel.

While the invention has been described, disclosed, illustrated and shownin various terms of certain embodiments or modifications which it haspresumed in practice, the scope of the invention is not intended to be,nor should it be deemed to be, limited thereby and such othermodifications or embodiments as may be suggested by the teachings hereinare particularly reserved especially as they fall within the breadth andscope of the claims here appended.

What is claimed is:
 1. A method for synthesizing first alkyl-adamantanefuel, comprising: providing a first isoprenoid and/or functionalizedisoprenoid feedstock; producing first mixture by hydrogenating saidfirst feedstock with hydrogen gas using at least one first hydrogenationcatalyst, wherein producing said first mixture further comprisesdistilling said first mixture to produce at least one sesquiterpane;producing a second mixture by isomerizing said first mixture from about0.3 hour to about 48 hours using a first acidic catalyst; and distillingsaid second mixture to produce said first alkyl-adamantine fuel.
 2. Themethod according to claim 1, wherein said producing said first mixturesaid hydrogenation catalyst further comprises at least onetransition-metal selected from the group consisting of nickel,palladium, platinum, ruthenium, and copper.
 3. The method according toclaim 1, wherein said producing said first mixture said hydrogenatingfurther comprises adding at least one polar solvent selected from thegroup consisting of ethyl acetate, other organic ester, acetic acid,other organic acid, methanol, ethanol, butanol, tetrahydrofuran (THF),dioxane, and other alcohols.
 4. The method according to claim 1, whereinsaid homogeneous acidic catalyst is selected from the group consistingof AlCl₃, FeCl₃, ZnCl₂, SbF₅, BF₃, Lewis acids based on Ti, V, Cr, Mn,Fe, Co, Ni, Cu, Zn, Al, B, Sn, Sb in various oxidation states, and otherhomogeneous Lewis-acid compounds.
 5. The method according to claim 4,wherein said producing said second mixture by said isomerizing furthercomprises adding at least one ionic liquid selected from the groupconsisting of pyridinium ionic liquid, imidazolium ionic liquid, acidicionic liquid, acidic chloroaluminate ionic liquid, clay-supportedchloroaluminate ionic liquid,[1-butyl-3-methylimidazolium][bis(trifluoromethylsulfonyl imide)],[1-butyl-3-methylimidazolium][tricyanomethanide],[tri(butyl)(tridecyl)phosphonium][bis(trifluoromethylsulfonylimide)],triethylammonium chloroaluminate, [1-butyl-3-methylpyridinium]chloroaluminate, and [1-butyl-3-methylimidazolium] chloroaluminate. 6.The method according to claim 1, wherein said acidic catalyst is aheterogeneous Lewis-acid selected from at least one of the groupconsisting of AlCl₃, FeCl₃, TiCl₄, ZnCl₂, SbF₅, BF₃, Lewis acids basedon Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Al, B, Sn, Sb in various oxidationstates, and other Lewis-acid compound, wherein said heterogeneous saidacidic catalyst is supported on at least one solid material selectedfrom the group consisting of zeolite, aluminosilicate, alumina,zirconia, titania, silica, and clay, other acidic metal oxide,cross-linked sulfonated polystyrene, other macroreticular resin, otheracidic polymer, crosslinked ionic liquid, crosslinked poly(ionicliquid), and crosslinked ionic liquid gel.
 7. The method according toclaim 1, wherein said producing said first mixture by hydrogenating saidfirst feedstock is from about 1 hour to 48 hours with hydrogen gas atpressures ranging from about 1 atm to about 50 atm using said firsthydrogenation catalyst at temperatures ranging from about 10° C. to 200°C. and wherein said producing said second mixture by isomerizing saidfirst mixture is from about 0.3 hour to about 48 hours using said firstacidic catalyst at pressures ranging from about 1 atm to about 10 atm attemperatures ranging from about 15° C. to about 350° C.
 8. The methodaccording to claim 1, wherein said fuel having a cetane number rangingfrom about 30 to about 42.